Interrelationships of trace metals in rat and mouse tissues will be studied as to effects of certain abnormal metals fed for life on tissue concentrations of chromium, manganese, copper and zinc. Effects of trace elements on the fertility and viability of offspring of breeding rats and mice constantly exposed to the metal from the time of weaning are being studied. Localization of toxic metals in subcellular components of mouse tissues, especially brains, of animals exposed to the metal for three generations are being studied. Life-term studies of rats exposed to low doses of trace elements are under way.